transport of protein (general stops)
ER—> ER-golgi intermediate compartment (ERGIC) –> golgi apparatus
exocytosis
membrane insertion
or lumenal aspects of lysosomes
Vesicles
transports proteins to and from ER and golgi (and can go to other parts of the cell)
vesicle passing is mitigated by …
signals on the protein
Golgi Structure
- not contiguous
- stacks of sacks (cisternae)
- has polarity on struc and function
-Cis face recieves from ERGIC
medial cisternae
middle of the stack
cisternae are usually…
swollen at the margins, where vesicles arise and fuse
Trans face faces …
away from the RER towards cell surface
trans-golgi network recieves from the trans face
the golgi complex
assembly line for modifying and packaging lumenal and transmembrane proteins
protein modifications
medial and trans compartments
–> removing/adding/ modifying carb and lipid components
—> covalently coupling protein and lipid components attach. to mem/secretory proteins
–> some proteins polymerize in the golgi
Lipid metabolism
med/trans compart.
–>convert ceramide (a base sphingolipid) into sphingomyelin or glycolipid
sorting proteins: trans golgi network
for delivery to their final cellular destination
Mod of Glycoproteins
- poly sacc added in the ER
- golgi mod to result in variety of glycoproteins serving spec functions (Mod depend on pro structure and enzymes available)
passing through golgi stacks
2 mech:
- cisternal Maturation model
- stable cisternae model
cisternal maturation model-
the entire stacks will move from cis to trans, maturing their proteins as they move
stable cisternae model
the stacks stay put, but send proteins from one stack to the next as the proteins mature
Vesicles formation and function
formed by membranes within cells
Move cargo and mem-bound proteins bt compartments w/in the cell
“pinching” the mem off each organelle to form a vesicle
Vesicular transport
selective!
coats assemble in the cytosol causing vesicles to bud off and separate
coats removed before delivery. vesicles fuse with target mem and empty their cargo, and insert their mem along with any mem proteins into target mem
steps of vesicular transport (coats)
- COP II-carry proteins from the ER–> ERGIC –>Golgi apparatus.
- COP I-coated vesicles bud from the ERGIC or Golgi and carry their cargo back, returning proteins to earlier compartments.
Clathrin and dynamin
triskeleton shape (trimer) base- induces curvature on plas mem when it polymerizes
when vesicle is sphericle dynamin comes to “pinch” it off to release ves into cytosol
forming GTP-binding proteins like ARF
Guanine nucleotide Exchange Factors (GEFs) activate ARF by exchanging GDP for GTP (ARF + GTP = active)
active GTP-bound ARF recruits…
Adaptor proteins that mediate vesicle assembly by interacting with cargo proteins and with coat proteins
- Adaptor proteins (AP) are what attaches the different coat proteins
- Different APs, different coats (this example is specific for clathrin.).
steps of budding and release
Activated and regulated by ARF and ARF-GEF
in GDP form- ARF is lazy
GTP form- causes vesicle formation
—> recruits clathrin
Dynamin pinches the stalk and clathrin unbinds
vesicle fusion step 1
- The vesicle must recognize the correct target membrane—> Rab proteins—> SNARES
